Process and equipment for the fractional desublimation of solids in vapor form from gas/vapor mixtures

Abstract

Solids are fractionally desublimed in vapor form from a gas/vapor mixture by providing a nozzle through which a gas/vapor mixture containing a solid is accelerated, the nozzle being provided with a concentric opening which allows a cooling gas flowing laterally at a high velocity to impinge upon and mix with the gas/vapor mixture flowing through the nozzle in the mixing zone of the nozzle thereby forming a gas/solid mixture, passing the gas/vapor mixture through the nozzle and the cooling gas through the concentric opening such that the angle at which the cooling gas emerges from the concentric opening into the flow of the gas/vapor mixture to the direction of flow of the gas/vapor mixture ranges from 0.17 pi rad to 0.75 pi rad, the temperature of the resulting gas/solid mixture in the mixing zone being adjusted by the flow rate of the cooling gas in such a way that the temperature is below the sublimation temperature of the desired product solid but above the sublimation temperature of the by-products in the gas/vapor mixture, and allowing the gas/solid mixture to exit the nozzle in the direction of flow of the gas/vapor mixture through the nozzle.

What is claimed as new and desired to be secured by Letters Patent of the United States is: 
     
       1. A process for fractionally desubliming solids in vapor form from a gas/vapor mixture, comprising: providing a nozzle through which a gas/vapor mixture containing a solid to be desublimed is accelerated, said nozzle provided with a concentric opening which allows a cooling gas flowing laterally at a high velocity to impinge upon and mix with the gas/vapor mixture flowing through said nozzle in the mixing zone of said nozzle, thereby forming a gas/solid mixture;   passing said gas/vapor mixture through said nozzle and said cooling gas through said concentric opening such that the angle at which the cooling gas emerges from the concentric opening into the flow of gas/vapor mixture to the direction of flow of the gas/vapor mixture ranges from 0.17 pi rad to 0.75 pi rad, the temperature of the resulting gas/solid mixture in the mixing zone being adjusted by the flow rate of the cooling gas in such a way that the temperature is below the sublimation temperature of the desired product solid but above the sublimation temperature of the byproducts in said gas/vapor mixture; and   allowing the gas solid mixture to exit said nozzle in the direction of flow of the gas/vapor mixture through the nozzle.   
     
     
       2. The process according to claim 1, wherein the flow velocities of the gas/vapor mixture and of the cooling gas are 10 to 200 m/second. 
     
     
       3. The process according to claim 2, wherein the flow velocities range from 20 to 150 m/second. 
     
     
       4. The process according to claim 1, wherein said angle between the direction in which the cooling gas emerges from the concentric opening and the direction of flow of the gas/vapor mixture is 0.5 pi rad. 
     
     
       5. The process according to claim 1, wherein said cooling gas is oxygen, nitrogen, carbon monoxide, carbon dioxide or mixtures thereof. 
     
     
       6. The process according to claim 1, wherein air is the cooling gas. 
     
     
       7. The process according to claim 1, wherein the flow velocity of said gas/solid mixture is 10 to 200 m/second. 
     
     
       8. The process according to claim 1, wherein the solid which is to be desublimed is a pyromellitic dianhydride. 
     
     
       9. An apparatus for fractionally desubliming solids in separate form from a gas/vapor mixture, comprising: a nozzle means progressively having a gas/vapor mixture inlet, a mixing zone having an interior surface, said gas/vapor mixture inlet having an orifice at the point in the nozzle where the gas/vapor mixture inlet joins the mixing zone, and a gas/solid mixture outlet, and   a concentric opening in said nozzle which permits inflow of a cooling gas laterally into the nozzle where the cooling gas impinges upon and mixes with said gas/vapor mixture in said mixing zone at said orifice, said concentric opening for the cooling gas being of variable geometry whose shape corresponds to the shape of said orifice.   
     
     
       10. The apparatus of claim 9, wherein the nozzle orifice is round of a diameter ranging from 2 to 12 mm. 
     
     
       11. The apparatus of claim 9, wherein the nozzle orifice is polygonal having a diagonal of 2 to 12 mm. 
     
     
       12. The apparatus of claim 9, wherein the nozzle orifice is slot-shaped having a slot width of 2 to 12 mm. 
     
     
       13. The apparatus of claim 9, wherein the dimensions of the mixing zone are exactly the same as the corresponding dimensions of the nozzle orifice for the gas/vapor mixture or are greater than these dimensions. 
     
     
       14. The apparatus of claim 13, wherein the mixing zone is further confined by an orifice plate which itself has an orifice, the shape of which plate corresponds to the shape of the nozzle for the gas/vapor mixture, with the orifice of the orifice plate being located opposite the orifice for the gas/vapor mixture. 
     
     
       15. The apparatus of claim 14, wherein said orifice plate consists of a heat resistant, dimensionally stable and heat-insulating material. 
     
     
       16. The apparatus of claim 9, wherein the opening for the cooling gas and the interior surface of the mixing zone consist of a heat-resistant, dimensionally stable and heat-insulating material. 
     
     
       17. The apparatus of claim 9, wherein the nozzle for the gas/vapor mixture consists of a material of high thermal conductivity. 
     
     
       18. The apparatus of claim 9, wherein the nozzle for the gas/vapor mixture is heated. 
     
     
       19. The apparatus of claim 9, wherein for high flow rates of gas/vapor mixture and cooling gas, a correspondingly large number of nozzle orifices for the gas/vapor mixture and openings for the cooling gas are provided in a compound arrangement and the resulting streams of gas/solid mixtures flow at said gas/solid outlets into a common chamber.